Multifunctional collimator for contact image sensors

ABSTRACT

Disclosed is a method to fabricate a multifunctional collimator structure In one embodiment, an optical collimator, includes: a dielectric layer; a substrate; and a plurality of via holes, wherein the dielectric layer is formed over the substrate, wherein the plurality of via holes are configured as an array along a lateral direction of a first surface of the dielectric layer, wherein each of the plurality of via holes extends through the dielectric layer and the substrate from the first surface of the dielectric layer to a second surface of the substrate in a vertical direction, wherein the substrate has a bulk impurity doping concentration equal to or greater than 1×10 19  per cubic centimeter (cm −3 ) and a first thickness, and wherein the bulk impurity doping concentration and the first thickness of the substrate are configured so as to allow the optical collimator to filter light in a range of wavelengths.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/655,763, filed Oct. 17, 2019, the entirety of which is incorporatedby reference herein.

BACKGROUND

In order to prevent noises from ambient infrared (IR) sources, a contactimage sensor (CIS), e.g., a finger print sensor, typically employs aglass filter. The glass filter in such application is typically thick(e.g., 400-500 micrometers) so as to provide efficient filtering ofambient IR noises especially at high incident angles (>15 degree). Thisresults in a bulky assembly and high cost. There exists a need todevelop a cost-effective method to filter ambient infrared light toreduce noises in contact image sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that various features are not necessarily drawn to scale. In fact,the dimensions and geometries of the various features may be arbitrarilyincreased or reduced for clarity of illustration.

FIG. 1 illustrates a flow chart of an exemplary method for forming asemiconductor device, in accordance with some embodiments of the presentdisclosure.

FIGS. 2A, 2B, 2C, 2D, 2E, and 2F, illustrate cross-sectional views of anexemplary semiconductor device with a collimator during variousfabrication stages, made by the method of FIG. 1 , in accordance withsome embodiments of the present disclosure.

FIG. 3 illustrates an exemplary cross-sectional views of a semiconductordevice with a collimator, in accordance with some embodiments of thepresent disclosure.

FIG. 4 illustrates exemplary cross-sectional views of sidewall profilesof etched openings in a collimator structure, in accordance with someembodiments of the present disclosure.

FIG. 5A illustrates an exemplary top view of a semiconductor device witha collimator, in accordance with some embodiments of the presentdisclosure.

FIG. 5B illustrates an exemplary top view of a semiconductor device witha collimator, in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following disclosure describes various exemplary embodiments forimplementing different features of the subject matter. Specific examplesof components and arrangements are described below to simplify thepresent disclosure. These are, of course, merely examples and are notintended to be limiting. For example, it will be understood that when anelement is referred to as being “connected to” or “coupled to” anotherelement, it may be directly connected to or coupled to the otherelement, or one or more intervening elements may be present.

A thick IR glass can be used to filter undesired ambient noises for aCIS sensor. This design results in a bulky structure and increases acost of such CIS sensor. This disclosure presents various embodiments ofa method for integrating a filter function to a collimator for contactimage sensors to simultaneously align incident light and filter ambientnoises with a compact design and low cost.

FIG. 1 illustrates a flowchart of a method 100 to form a multifunctionalcollimator structure on a semiconductor device, in accordance with someembodiments of the present disclosure. It is noted that the method 100is merely an example, and is not intended to limit the presentdisclosure. Accordingly, it is understood that additional operations maybe provided before, during, and after the method 100 of FIG. 1 , andthat some other operations may only be briefly described herein. In someembodiments, operations of the method 100 may be associated withcross-sectional views of a semiconductor device at various fabricationstages as shown in FIGS. 2A, 2B, 2C, 2D, 2E, and 2F, respectively, whichwill be discussed in further detail below.

Referring now to FIG. 1 , the method 100 starts with operation 102 inwhich a first substrate is provided according to some embodiments. Insome embodiments, the first substrate comprises at least one opticalsensing element and at least one conductive feature for contactingpurposes. The method 100 continues with operation 104 in which a firstdielectric layer is deposited on the surface of the first substrateaccording to some embodiments. In some embodiments, the first dielectriclayer comprises silicon dioxide is for planarization purposes. In someembodiments, the first dielectric layer also provides a Si-to-oxidefusion-bond surface. In some embodiments, a shallow opening (i.e.,partial etching in the first dielectric layer) is also performed. Themethod 100 continues with operation 106 in which a second substrate isbonded over the first dielectric layer on the first substrate accordingto some embodiments. In some embodiments, the second substrate is bondedto the first dielectric layer through a wafer bonding process. In someembodiments, the second substrate is a p-type or n-type siliconsubstrate with a bulk impurity doping level equal to or greater than1×10¹⁹ cm⁻³. The method 100 continues with operation 108 in which thesecond substrate is thinned down according to some embodiments. In someembodiments, the thinned second substrate has a thickness, wherein thethickness is equal to or greater than 75 micrometers. The method 100continues with operation 110 in which a second dielectric layer isdeposited on a first surface of the thinned second substrate accordingto some embodiments. In some embodiments, the second dielectric layercomprises silicon dioxide. The method 100 continues with operation 112in which a photoresist layer is patterned on the second dielectric layeraccording to some embodiments. In some embodiments, the patternedphotoresist layer provides a pattern of a collimator structure. Themethod 100 continues with operation 114 in which a plurality of viaholes through the second dielectric layer and the thinned secondsubstrate is formed according to some embodiments. In some embodiments,the plurality of via holes is formed by etching the second dielectriclayer using the patterned first photoresist layer as a soft maskfollowed by etching the thinned second substrate using the patternedsecond dielectric layer as a hard mask. In some embodiments, at leastone opening is also etched in the first dielectric layer so as to exposethe at least one conductive feature in the first substrate forcontacting purposes. In some embodiments, a chemical etching process isperformed so as to remove the photoresist layer. In some embodiments,the semiconductor device with the first substrate and the collimatorstructure through the second dielectric layer and the thinned secondsubstrate is then wafer diced to form a plurality of dies. In someembodiments, each of the plurality of dies is then wafer bonded to athird substrate and further wire bonded. In some embodiments, each ofthe plurality of dies is embedded in a molding and packaged.

As mentioned above, FIGS. 2A-2F illustrate, in a cross-sectional view, aportion of a semiconductor device 200 at various fabrication stages ofthe method 100 of FIG. 1 . The semiconductor device 200 may be includedin an integrated circuit (IC). Also, FIGS. 2A-2F are simplified for abetter understanding of the concepts of the present disclosure. Althoughthe figures illustrate the semiconductor device 200, it is understoodthe IC may comprise a number of other devices such as resistors,capacitors, inductors, fuses, etc., which are not shown in FIGS. 2A-2F,for purposes of clarity of illustration.

FIG. 2A is a cross-sectional view of the semiconductor device 200including a first substrate 202 and a first dielectric layer 204 at oneof the various stages of fabrication corresponding to operations 102 and104 of FIG. 1 , in accordance with some embodiments of the presentdisclosure. In some embodiments, the first substrate 202 comprises atleast one optical sensing element (not shown) in an optical sensingelement region 208. In some embodiments, the at least one opticalsensing element each is a Contact Image Senor (CIS). In someembodiments, the CIS is an image sensor used in direct contact with theobject to be imaged or scanned. In some embodiments, the CIS comprises aplurality of detectors. In some embodiments, the plurality of detectorsdetects light directed from an object surface. In some embodiments, theplurality of detectors each comprises one of the following: a ChargeCoupled Device (CCD) sensor and a Complementary metal-oxidesemiconductor (CMOS) sensor. In some embodiments, the first substrate202 further comprises 2 conductive features 206.

In some embodiments, the first substrate 202 is a silicon substrate.Alternatively, the first substrate 202 may include other elementarysemiconductor material such as, for example, germanium. The firstsubstrate 202 may also include a compound semiconductor such as siliconcarbide, gallium arsenic, indium arsenide, and indium phosphide. Thefirst substrate 202 may include an alloy semiconductor such as silicongermanium, silicon germanium carbide, gallium arsenic phosphide, andgallium indium phosphide. In one embodiment, the first substrate 202includes an epitaxial layer. For example, the first substrate 202 mayhave an epitaxial layer overlying a bulk semiconductor. Furthermore, thefirst substrate 202 may include a semiconductor-on-insulator (SOI)structure. For example, the first substrate 202 may include a buriedoxide (BOX) layer formed by a process such as separation by implantedoxygen (SIMOX) or other suitable technique, such as wafer bonding andgrinding.

In some embodiments, the first substrate 202 also includes variousp-type doped regions and/or n-type doped regions, implemented by aprocess such as ion implantation and/or diffusion. Those doped regionsinclude n-well, p-well, lightly doped region (LDD), heavily doped sourceand drain (S/D), and various channel doping profiles configured to formvarious integrated circuit (IC) devices, such as a CMOS field-effecttransistor (CMOS-FET), imaging sensor, and/or light emitting diode(LED). The first substrate 202 may further include other functionalfeatures such as a resistor or a capacitor formed in and on thesubstrate. The first substrate 202 further includes lateral isolationfeatures provided to separate various devices formed in the firstsubstrate 202, for example shallow trench isolation (STI). The variousdevices in the first substrate 202 further include silicide disposed onS/D, gate and other device features for reduced contact resistance andenhance process compatibility when coupled between devices through localinterconnections.

In some embodiment, at least one conductive feature is included in thefirst substrate 202. In some embodiments, the at least one conductivefeature can be a source, drain or gate electrode. Alternatively, the atleast one conductive feature may be a silicide feature disposed on asource, drain or gate electrode typically from a sintering processintroduced by at least one of the processes including thermal heating,laser irradiation or ion beam mixing. The silicide feature may be formedon polysilicon gate (typically known as “polycide gate”) or by onsource/drain (typically known as “salicide”) by a self-aligned silicidetechnique. In another embodiment, the at least one conductive featuremay include an electrode of a capacitor or one end of a resistor. Inanother embodiment, the at least one conductive feature is a contact tothe CIS sensor in the first substrate 202.

In some embodiments, the first dielectric layer 204 comprises a materialthat is at least one of the following: silicon dioxide, a low dielectricconstant (low-k) material, other suitable dielectric material, or acombination thereof. The low-k material may include fluorinated silicaglass (FSG), phosphosilicate glass (PSG), borophosphosilicate glass(BPSG), carbon doped silicon oxide (SiO_(x)C_(y)), Black Diamond®(Applied Materials of Santa Clara, Calif.), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), SILK (DowChemical, Midland, Mich.), polyimide, and/or other future developedlow-k dielectric materials. In some embodiments, the first dielectriclayer 204 is deposited using plasma enhanced chemical vapor deposition(PECVD) with a silane gas as a precursor gas. In some other embodiments,the first dielectric layer 204 is deposited using a physical vapordeposition (PVD) process.

FIG. 2B is a cross-sectional view of the semiconductor device 200including the first substrate and the first dielectric layer 204 at oneof the various stages of fabrication that corresponds to operation 104of FIG. 1 , in accordance with some embodiments. In the illustratedembodiment, 2 shallow openings 210 in the first dielectric layer 204 atpositions corresponding to the 2 conductive features in the firstsubstrate 202 are created. In some embodiments, a photolithographicprocess is performed and a dry or wet etching is used to perform apartial etching in the first dielectric layer.

FIG. 2C is a cross-sectional view of the semiconductor device 200including the first substrate 202, the first dielectric layer 204 and asecond substrate 206 at one of the various stages of fabrication thatcorresponds to operation 106 of FIG. 1 , in accordance with someembodiments of the present disclosure. In some embodiments, the secondsubstrate 206 includes a silicon substrate. In some embodiments, thesecond substrate 212 is a p-type substrate or an n-type substrate withan impurity doping level (i.e., carrier concentration) equal to orgreater than 1×10¹⁹ cm⁻³. A high concentration of impurity doping in thesecond substrate results in an increased light absorption in the nearInfrared (IR) region due to a band gap shift, which affects bothphonon-assisted absorption, and free-carrier absorption. Therefore, theuse of the second substrate with a high carrier concentration can beused to reduce noise by limiting the ambient near IR light from reachingthe at least one optical sensing element in the first substrate.Alternatively, the second substrate 206 may include other elementarysemiconductor material according to the optical properties of thematerials, such as, for example, germanium. The second substrate 206 mayalso include a compound semiconductor such as silicon carbide, galliumarsenic, indium arsenide, and indium phosphide. The second substrate 206may include an alloy semiconductor such as silicon germanium, silicongermanium carbide, gallium arsenic phosphide, and gallium indiumphosphide. In some embodiments, a selection of the second substrate andits impurity doping concentration can be determined according to adesired working wavelength range, e.g., between 780 nanometers and 1100nanometers. In one embodiment, the second substrate 206 includes anepitaxial layer. For example, the second substrate 206 may have anepitaxial layer overlying a bulk semiconductor. Furthermore, the secondsubstrate 206 may include a semiconductor-on-insulator (SOI) structure.For example, the second substrate 206 may include a buried oxide (BOX)layer formed by a process such as separation by implanted oxygen (SIMOX)or other suitable technique, such as wafer bonding and grinding.

In some embodiments, the second substrate 212 is bonded to the firstdielectric layer 204 in a region corresponding to the optical sensingregion 208 through a wafer bonding process. In some embodiments, thewafer bonding process is a direct bonding without any additionalintermediate layers. In some embodiments, the wafer bonding processcomprises at least one of the following steps: surface preprocessing,pre-bonding at room temperature, and annealing at elevated temperatures.In another embodiment, surface activation can be used so as to avoidhigh temperature annealing.

FIG. 2D is a cross-sectional view of the semiconductor device 200including a second dielectric layer 214 over a thinned second substrate212′ at one of the various stages of fabrication that corresponds tooperations 108 and 110 of FIG. 1 , in accordance with some embodimentsof the present disclosure. In some embodiments, the second substrate 212after bonding to the first dielectric layer 204 on the first substrate202 is further thinned down to obtain a first thickness, wherein thefirst thickness is determined according to an absorption coefficient inthe desired filtering wavelength range (between 780 nanometers and 1100nanometers). In some embodiments, the absorption coefficient in cm⁻¹ ofthe second substrate 212 is a function of the impurity dopingconcentration of the second substrate and its bandgap. For example, whenthe second substrate is a silicon substrate, with an increasing dopingconcentration, the band gap of the second substrate reduces and theabsorption coefficient increases. In some embodiments, the secondsubstrate 206 is etched by a dry and/or wet etching process. In someembodiments, the thinned second substrate 212′ has a thickness which isequal to or greater than 75 micrometer. In some embodiments, the seconddielectric layer 214 is deposited on the thinned second substrate 212.In some embodiments, the second dielectric layer 214 comprises amaterial that is least one of the following: silicon dioxide, a lowdielectric constant (low-k) material, other suitable dielectricmaterial, or a combination thereof. The low-k material may includefluorinated silica glass (FSG), phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), carbon doped silicon oxide(SiO_(x)C_(y)), Black Diamond® (Applied Materials of Santa Clara,Calif.), Xerogel, Aerogel, amorphous fluorinated carbon, Parylene, BCB(bis-benzocyclobutenes), SiLK (Dow Chemical, Midland, Mich.), polyimide,and/or other future developed low-k dielectric materials. In someembodiments, the second dielectric layer 208 is deposited using plasmaenhanced chemical vapor deposition (PECVD) with a silane gas as aprecursor gas. In some other embodiments, the second dielectric layer208 is deposited using a physical deposition process, e.g., sputteringand evaporation. In some embodiments, the second dielectric layer 214 isdeposited using an atomic layer deposition (ALD) process. In someembodiments, the second dielectric layer 214 has a thickness equal to orgreater than 3 micrometers. In some embodiments, the surface of thesecond substrate that is not in direct contact with the first dielectriclayer 204 after etching is further planarized through aChemical-Mechanical Polishing (CMP) process before the deposition of thesecond dielectric layer 214.

FIG. 2E is a cross-sectional view of the semiconductor device 200 inwhich a photoresist layer 216 is patterned on the second dielectriclayer 214 at one of the various stages of fabrication that correspondsto operation 112 of FIG. 1 , in accordance with some embodiments of thepresent disclosure. As described below, the patterned photoresist layer216 with a plurality of openings 218 is used to mask an etching of thesecond dielectric layer 214 and the thinned second substrate 212′ toform a plurality of via holes (i.e., a collimator structure) on top ofthe first dielectric layer 204 on the first substrate 202. Accordingly,in some embodiments, the patterned photoresist layer 216 is formed aftera conventional patterning (e.g., photolithography) process, to align thecollimate structure with the at least one optical sensing element in theoptical sensing region 208 of the first substrate 202.

In some embodiments, an initial photoresist layer 216 before thepatterning process may include a negative or positive tone photoresistlayer that is patternable in response to a photolithography lightsource. In some alternative embodiments, the initial photoresist layer210 may include an e-beam (electron beam) resist layer (e.g., polymethyl methacrylate, methyl methacrylate, etc.) that is patternable inresponse to an e-beam lithography energy source. In some embodiments,the initial photoresist layer 216 is formed over the second dielectriclayer 214 using a deposition process known in the art such asspin-coating, spray-coating, dip-coating, roller-coating, or the like.The initial photoresist layer 216 is then patterned in a lithographyprocess that may involve various exposure, developing, baking,stripping, etching, and rinsing processes. As a result, the patternedphotoresist layer 216 is formed such that a plurality of openings 218expose at least a portion of the top surface of the second dielectriclayer 214, as shown in FIG. 2E. In some embodiments, the plurality ofopenings 218 in the patterned photoresist layer 216 is circular and hasa diameter of 4.2 micrometers. In some embodiments, the diameters of theplurality of openings 218 are in a range of 2-5 micrometers.

FIG. 2F is a cross-sectional view of the semiconductor device 200 inwhich a plurality of via holes 220 is formed in the second dielectriclayer 214 and the thinned second substrate 212′, the patternedphotoresist layer 216 is removed and at least one conductive feature 206is exin the posed through the first dielectric layer 204 at one of thevarious stages of fabrication that corresponds to operations 114 of FIG.1 , in accordance with some embodiments of the present disclosure. Insome embodiments, the second dielectric layer 214 is first etched so asto transfer the pattern of the plurality of openings 218 in thepatterned photoresist layer 216 to the second dielectric layer 214. Insome embodiments, the thinned second substrate 212′ is then furtheretched through the patterned second dielectric layer 214 so as totransfer the patterns in the second dielectric layer 214 to the thinnedsecond substrate 212′. In some embodiments, the etching of the seconddielectric layer 214 and the thinned second substrate 212′ is performedby a dry and/or wet etching process.

In some embodiments, the patterned photoresist layer 216 is removedbefore the etching of the thinned second substrate 212′. In someembodiments, the patterned photoresist layer 216 may be removed by oneor more chemical cleaning processes using acetone, 1-Methyl-2-pyrrolidon(NMP), Dimethyl sulfoxide (DMSO), or other suitable removing chemicals.In some embodiments, the chemicals used may need to be heated totemperatures higher than room temperature to effectively dissolve thepatterned photoresist layer 216. The selection of the remover isdetermined by the type and chemical structure of the patternedphotoresist layer 216, the second dielectric layer 214, as well as thethinned second substrate 212′ to assure the chemical compatibility ofthese layers with the chemical cleaning process. In some embodiments,this cleaning process is then followed by a rinsing process usingisopropyl alcohol or the like, followed by rinsing using deionizedwater. As a result of this process, the plurality of via holes 220,i.e., the collimator structure, are formed through the second dielectriclayer 214 and the thinned second substrate 212′. In some embodiments,the collimator structure comprises a top surface 222 of the seconddielectric layer 214 and sidewalls 224. In some embodiments, the atleast one conductive feature 206 is exposed by etching the 2 partialopenings 210 in the first dielectric layer 204 so as to provide anelectric contact to the at least one optical sensing element in theoptical sensing region 208 in the first substrate 202 using a wet or dryetching process.

In some embodiments, the collimator structure narrows incident light andallow the incident light to be aligned in a specific direction when thelight arrives at the at least one optical sensing element in the opticalsensing region 208 of the first substrate 202. Furthermore, thecollimator structure created in the thinned second substrate 212′ withan impurity doping concentration equal to or greater than 1×10¹⁹ cm⁻³further allows to filter undesired ambient noises (e.g., near IR light)and prevent these noises from reaching the at least one optical sensingelement. Therefore, the collimator structure in the present disclosureprovides multiple functions allowing the use of regular glass duringpackaging and thus reducing the cost, and further allowing the use ofCIS devices in space-limited applications.

FIG. 3 illustrates an exemplary cross-sectional view of a semiconductordevice 300 with a collimator structure, in accordance with someembodiments of the present disclosure. In the illustrated embodiment,the collimator structure is fabricated according to the method 100described in FIG. 1 . Specifically, the device 300 comprises a firstsubstrate 202 with an optical sensing region 208, a first dielectriclayer 204, and a plurality of via holes 220 in a thinned secondsubstrate 212′ and a second dielectric layer 214.

In some embodiments, the patterned second dielectric layer 214 has athickness 302 in a range of 1.5-2.5 micrometers. In some embodiments,the thinned second substrate 212′ has a thickness 304 in a range of72-78 micrometers. In some embodiments, a diameter 306 of each of theplurality of via holes 220 is in a range of 3-5 micrometers. In someembodiments, a pitch size 308 is in a range of 2.6-3.4 micrometers.

In the illustrated embodiment, the sidewalls 310 of the plurality of viaholes 220 etched into the second dielectric layer 214 and the thinnedsecond substrate 212′ are perpendicular to the exposed surface of thefirst dielectric layer 204. This profile obtained under ideal etchingconditions with idea sidewalls passivation in the device 300 is forillustration purposes and not intend to be limiting. Practical etchingconditions (i.e., etching rate in different directions) can causeeffects such as tapering, undercutting, notching, bowing, rippling,etc., which alter the sidewall profile of the openings 220. It should benoted that different sidewall profiles that can be obtained frompractical etching conditions are all within the scope of this invention.

FIG. 4 illustrates various sidewall profiles 400 of a via hole etched ina second dielectric layer 214 and a thinned second substrate 212′ in asemiconductor device 300, in accordance with some embodiments of thepresent disclosure. The various sidewall profiles 400 comprises a firstprofile 402 with vertical sidewalls 310 from an ideal etching condition,a second profile 404 with tapered sidewalls 310 and complete undercuts416 under the second dielectric layer 214 caused by a strong sidewallpassivation, a third profile 406 with tapered sidewalls 310 and partialundercuts 416 under the second dielectric layer 214 caused by aspontaneous etching reaction, a fourth profile 408 with sidewalls 310comprising ripples 418, a fifth profile 410 with smoothly curvedsidewalls 310, a sixth profile 412 with tapered sidewalls 310 andnotches 420 at the bottom of the via hole in the thinned secondsubstrate 212′ caused by distorted ion trajectories and/or chemicaletching, a seventh profile 414 with inverted tapering sidewalls 310, andan eighth profile 416 with tapered sidewalls 310 and eroded corners 422in the second dielectric layer 214. It should be noted that sidewallprofiles in the FIG. 4 is for illustration purposes and not intended tobe limiting. Different sidewall profiles that can be obtained fromvarious etching conditions are all within the scope of this invention.It should be noted FIG. 4 is for illustration purposes and is notintended to be limiting. Different profiles of the sidewalls 310 of thevia holes 220 can be fabricated and used, which are within the scope ofthis invention.

FIG. 5A illustrates an exemplary top view of a semiconductor device 500with a collimator structure, in accordance with some embodiments of thepresent disclosure. The collimator structure in the device 500 comprises64 via holes 220. In the illustrated embodiments, the via holes 220 eachhas a circular cross section. In some other embodiments, differentshapes (e.g., square) of cross sections of the via holes 220 can be usedand are within the scope of this invention. In the illustratedembodiments, the via holes 220 are arranged in a 8×8 array with a squareunit cell 502. It should be noted the device 500 in FIG. 5A is forillustration purposes, any numbers of via holes 220 can be used and iswithin the scope of this invention.

FIG. 5B illustrates an exemplary top view of a semiconductor device 500with a collimator structure, in accordance with some embodiments of thepresent disclosure. The collimator structure in the device 500 comprises60 via holes 220. In the illustrated embodiments, the via holes 220 eachhas a circular cross section. In some other embodiments, differentshapes (e.g., square) of cross sections of the via holes 220 can be usedand are within the scope of this invention. In the illustratedembodiments, the via holes 220 are arranged in an array with a diamondunit cell 504. It should be noted the device 500 in FIG. 5A is forillustration purposes, any numbers of via holes 220 can be used and iswithin the scope of this invention.

In one embodiment, an optical collimator, includes: a dielectric layer;a substrate; and a plurality of via holes, wherein the dielectric layeris formed over the substrate, wherein the plurality of via holes areconfigured as an array along a lateral direction of a first surface ofthe dielectric layer, wherein each of the plurality of via holes extendsthrough the dielectric layer and the substrate from the first surface ofthe dielectric layer to a second surface of the substrate in a verticaldirection, wherein the substrate has a bulk impurity dopingconcentration equal to or greater than 1×10¹⁹ per cubic centimeter(cm⁻³) and a first thickness, and wherein the bulk impurity dopingconcentration and the first thickness of the substrate are configured soas to allow the optical collimator to filter light in a range ofwavelengths.

In another embodiment, a semiconductor device, includes: at least oneoptical sensing element; and an optical collimator; wherein the opticalcollimator comprises: a first dielectric layer, a first substrate, and aplurality of via holes, wherein the first dielectric layer is formedover the first substrate, wherein the plurality of via holes areconfigured as an array along a lateral direction of a first surface ofthe first dielectric layer, wherein each of the plurality of via holesextends through the first dielectric layer and the first substrate fromthe first surface of the first dielectric layer to a second surface ofthe first substrate in a vertical direction, wherein the first substratehas a bulk impurity doping concentration equal to or greater than 1×10¹⁹per cubic centimeter (cm⁻³) and a first thickness, and wherein the bulkimpurity doping concentration and the first thickness of the firstsubstrate are configured so as to allow the optical collimator to filterlight in a range of wavelengths.

Yet, in another embodiment, a method for forming a semiconductor device,includes: forming a collimator structure on a first substrate with afirst dielectric layer, wherein the collimator structure comprises aplurality of via holes, wherein each of the plurality of via holesextends through a second dielectric layer and a second substrate from afirst surface of the second dielectric layer to a second surface of thesecond substrate in a vertical direction, wherein the second substratehas a bulk impurity doping concentration equal to or greater than 1×10¹⁹per cubic centimeters (cm⁻³) and a first thickness, and wherein the bulkimpurity doping concentration and the first thickness of the secondsubstrate are configured so as to allow the collimator structure tofilter light in a range of wavelengths.

The foregoing outlines features of several embodiments so that thoseordinary skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. An optical collimator, comprising: a dielectriclayer; a substrate; and a plurality of via holes, wherein the dielectriclayer is formed over the substrate, wherein the plurality of via holesare configured as an array along a lateral direction of a first surfaceof the dielectric layer, wherein each of the plurality of via holesextends through the dielectric layer and the substrate from the firstsurface of the dielectric layer to a second surface of the substrate ina vertical direction, wherein a bulk impurity doping concentration and afirst thickness of the substrate are configured so as to allow theoptical collimator to filter light in a range of wavelengths between 780and 1100 nanometers.
 2. The optical collimator of claim 1, wherein thesubstrate comprises silicon.
 3. The optical collimator of claim 1,wherein the first thickness of the substrate is equal to or greater than75 micrometers.
 4. The collimator of claim 1, wherein a second thicknessof the dielectric layer is in a range of 1.5-2.5 micrometer.
 5. Thecollimator of claim 1, wherein each of the plurality of via holes has adiameter in a range of 3-5 micrometers.
 6. The collimator of claim 1,wherein the dielectric layer comprises silicon dioxide.
 7. Thecollimator of claim 1, wherein the substrate has a bulk impurity dopingconcentration equal to or greater than 1×10¹⁹ per cubic centimeter(cm⁻³).
 8. A semiconductor device, comprising: at least one opticalsensing element; and an optical collimator; wherein the opticalcollimator comprises: a first dielectric layer, a first substrate, and aplurality of via holes, wherein the first dielectric layer is formedover the first substrate, wherein the plurality of via holes areconfigured as an array along a lateral direction of a first surface ofthe first dielectric layer, wherein each of the plurality of via holesextends through the first dielectric layer and the first substrate, andwherein a bulk impurity doping concentration and a first thickness ofthe first substrate are configured so as to allow the optical collimatorto filter light in a range of wavelengths between 780 and 1100nanometers.
 9. The semiconductor device of claim 8, wherein the at leastone optical sensing element is formed in a second substrate, wherein thesecond substrate is further coated with a second dielectric layer, andwherein the optical collimator is formed over the second dielectriclayer.
 10. The semiconductor device of claim 8, wherein the firstsubstrate comprises silicon.
 11. The semiconductor device of claim 8,wherein a first thickness of the first substrate is equal to or greaterthan 75 micrometers.
 12. The semiconductor device of claim 8, wherein asecond thickness of the first dielectric layer is in a range of 1.5-2.5micrometer.
 13. The semiconductor device of claim 8, wherein each of theplurality of via holes has a diameter in a range of 3-5 micrometers. 14.The semiconductor device of claim 8, wherein the first dielectric layercomprises silicon dioxide.
 15. The semiconductor device of claim 8,wherein the first substrate has a bulk impurity doping concentrationequal to or greater than 1×10¹⁹ per cubic centimeter (cm⁻³).
 16. Amethod for forming a semiconductor device, comprising: forming acollimator structure on a first substrate with a first dielectric layer,wherein the collimator structure comprises a plurality of via holes,wherein each of the plurality of via holes extends through a seconddielectric layer and a second substrate in a vertical direction, whereinthe second substrate is formed over the first dielectric layer and thesecond dielectric layer is formed over the second substrate, and whereinthe bulk impurity doping concentration and the first thickness of thesecond substrate are configured so as to allow the collimator structureto filter light in a predetermined range of wavelengths.
 17. The methodof claim 16, further comprising: prior to the forming, bonding thesecond substrate to the first dielectric layer on the first substrate,wherein the first substrate comprises at least one optical sensingelements, wherein the at least one optical sensing elements aligns withthe collimator structure, and wherein the first dielectric layer isconfigured between the collimator structure and the first substrate. 18.The method of claim 16, wherein , and wherein the second substrate has abulk impurity doping concentration equal to or greater than 1×10¹⁹ percubic centimeters (cm⁻³) and the predetermined range of wavelengths isbetween 780 and 1100 nanometers.
 19. The method of claim 16, wherein thefirst thickness of the second substrate is equal to or greater than 75micrometers and a second thickness of the second dielectric layer is ina range of 1.5-2.5 micrometer.
 20. The method of claim 16, wherein eachof the plurality of via holes has a diameter in a range of 3-5micrometers.